{"id":493,"date":"2020-10-08T16:07:08","date_gmt":"2020-10-08T14:07:08","guid":{"rendered":"https:\/\/auroralabsnorway.com\/blog\/?p=493"},"modified":"2023-09-23T09:32:25","modified_gmt":"2023-09-23T07:32:25","slug":"twilight-occurrence","status":"publish","type":"post","link":"https:\/\/auroralabsnorway.com\/blog\/twilight-occurrence\/","title":{"rendered":"Twilight Occurrence"},"content":{"rendered":"\n

In a previous article<\/a> we saw what is twilight and what are the main types of twilight. As a reminder, twilight is the period of the day when a certain point on Earth is illuminated indirectly, by sunlight scattering, when the Sun is below the horizon, but not more than 18\u00b0, thus its rays are still visible, indirectly, for an observer located at that certain point.<\/p>\n\n\n\n

Now, we’re going to look at how twilight occurs on Earth, when it occurs and… how it doesn’t occur at all in certain places! <\/p>\n\n\n\n

Standard twilight occurrence<\/h2>\n\n\n\n

A standard twilight occurrence was described in our previous article: <\/p>\n\n\n\n

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During the course of a day, at sunrise, the Sun appears in the sky from the right (East) and, during the whole daytime, it shines its light directly onto the place on Earth where the observer is located. In the evening, at sunset, the Sun will again reach 0\u00b0 on the left side (West) and it will slowly disappear under the horizon. This moment the evening twilight<\/em> starts. Due to earth\u2019s rotation, the Sun will continue to descend more and more under the horizon. But before our star reaches 18\u00b0 under the horizon, there will still be distinguishable light from the Sun for the observer. When the Sun reaches 18\u00b0, dusk<\/em> occurs, and the observer will not distinguish any indirect sunlight anymore and the astronomical night starts.<\/p>\n\n\n\n

Because of Earth\u2019s rotation, the Sun continues its trip and, very early in the morning, before it rises, it will reach again 18\u00b0 under the horizon. At this moment, dawn<\/em> occurs, and twilight starts again \u2013 this time we\u2019re talking about the morning twilight<\/em>. As time passes more, the Sun will ascend more, until it reaches again 0\u00b0 and it rises the next day.<\/p>\n\n\n\n

Twilight occurs thus during both periods of the day when the Sun is between 0\u00b0 and 18\u00b0 under the horizon.<\/p>\n\n\n\n

This scenario is true for people living on Earth between approximately 50\u00b0 North or South of the Equator at any time of the year. This is also valid for higher latitudes, but not<\/strong> around the summer solstice, when the Sun does not descend more than 18\u00b0 under the horizon during the “night”, and thus there’s no real astronomical night between dusk and dawn.<\/p>\n\n\n\n

Continuous twilight between sunset and sunrise<\/h2>\n\n\n\n

As written in the previous paragraph, above latitudes of approximately 50\u00b0N\/S, around the date of the summer solstice<\/strong>, the Sun does not descend lower than 18\u00b0 under the horizon, which means that, even if the Sun is under the horizon, its rays can still be seen, indirectly, during the whole night, which translates itself into a continuous twilight during the whole “night” hours.<\/p>\n\n\n\n

In function of the latitude, there can be a continuous astronomical twilight, a continuous nautical twilight, or a continuous civil twilight between sunset and sunrise. This actually occurs in very popular and accessible places around the world, such as:<\/p>\n\n\n\n